US4861209A - Threaded coupling - Google Patents
Threaded coupling Download PDFInfo
- Publication number
- US4861209A US4861209A US07/073,801 US7380187A US4861209A US 4861209 A US4861209 A US 4861209A US 7380187 A US7380187 A US 7380187A US 4861209 A US4861209 A US 4861209A
- Authority
- US
- United States
- Prior art keywords
- range
- thread
- internal
- pitch
- crown
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- 230000008878 coupling Effects 0.000 title claims abstract description 17
- 238000010168 coupling process Methods 0.000 title claims abstract description 17
- 238000005859 coupling reaction Methods 0.000 title claims abstract description 17
- 238000009527 percussion Methods 0.000 claims abstract description 4
- 229910000831 Steel Inorganic materials 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 238000005553 drilling Methods 0.000 description 2
- 239000010959 steel Substances 0.000 description 2
- 230000001464 adherent effect Effects 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
Images
Classifications
-
- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B17/00—Drilling rods or pipes; Flexible drill strings; Kellies; Drill collars; Sucker rods; Cables; Casings; Tubings
- E21B17/02—Couplings; joints
- E21B17/04—Couplings; joints between rod or the like and bit or between rod and rod or the like
- E21B17/042—Threaded
- E21B17/0426—Threaded with a threaded cylindrical portion, e.g. for percussion rods
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T403/00—Joints and connections
- Y10T403/57—Distinct end coupler
- Y10T403/5746—Continuous thread
Definitions
- the present invention relates to a threaded coupling having a diameter in the interval of 30 to 40 mm adapted for percussion drill rods and comprising an external thread on the rod and an internal thread in the sleeve, the threads both of the rod and the sleeve having continuously curved tops and bottoms in the longitudinal section of said threads.
- the R16-profile has a good fatigue resistance in combination with a satisfying wearability thanks to the rounded shape of tops and bottoms of the thread.
- the problem is that the thread coupling due to the high percussion frequency does not stay sufficiently tightened during work. This means that the degree of efficiency for the energy of the shock wave decreases and so-called pittings develop on the contact surfaces of the thread. These pittings do eventually lead to a fatigue fracture.
- the aim of the invention is thus to prevent a thread coupling that remains sufficiently tightened during work without deteriorating the good characteristics in fatigue resistance and wearability.
- FIGS. 1a and 1b disclose certain geometric parameters in connection with threads
- FIG. 2 discloses schematically the geometry of a so-called rope thread
- FIGS. 3a and 3b disclose a diagram of how the tightening capacity varies with the pitch and the shoulder angle.
- the tightening capacity of a thread can be defined as the ratio between the uncoupling torque, MU, and the tightening torque, MT.
- FIGS. 1a and 1b The geometric quantities of the formula (1) are disclosed in FIGS. 1a and 1b.
- a characterizing feature for rope threads is that they have a constant radius of curvature both at the thread top and its bottom.
- these constant radii of curvature are designated by R 1 and R 2 , respectively.
- the primary aim of the present invention is thus to increase the tightening capacity of a thread coupling, i.e. ##EQU4## shall relatively seen have as high a value as possible.
- a thread coupling i.e. ##EQU4## shall relatively seen have as high a value as possible.
- the characteristics concerning fatigue resistance and wearability in a negative way one must also consider the relative magnitude of the height and radius of curvature of the thread.
- the embodiment according to FIGS. 3a and 3b refers to a so-called asymmetrical thread, the thread coupling having a maximum diameter DyM of 38 mm.
- the shoulder that has no contacting function in the thread coupling is made as short as possible.
- the asymmetrical thread according to FIGS. 3a and 3b has the advantage of a relatively seen smaller pitch S that leads to a better tightening property than a conventional rope thread having the same parameters for the working thread shoulder, i.e. where contact is present.
- the external thread on the rod 10R according to FIG. 3a has a height H 1 equal to 1.50 mm, the pitch S is equal to 9.28 mm, the radius of curvature R 1 for the top or crown 12R of the thread is 3.5 mm, and the radius of curvature R 2 for the bottom or root 14R of the thread is 4.0 mm.
- the internal thread of the sleeve 10S according to FIG. 3b has a height H 2 of 1.435 mm, a pitch S of 9.28 mm, a radius of curvature R 3 for the top 12S of thread of 5.0 mm, and a radius of curvature R 4 for the bottom 14S of the thread of 3.5 mm.
- the diagram of FIG. 4 discloses how the tightening capacity ##EQU6## varies with the parameters for pitch S and shoulder angle, said angle in itself including the parameters of radius of curvature and height.
Landscapes
- Engineering & Computer Science (AREA)
- Geology (AREA)
- Mining & Mineral Resources (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Life Sciences & Earth Sciences (AREA)
- Fluid Mechanics (AREA)
- Environmental & Geological Engineering (AREA)
- Physics & Mathematics (AREA)
- Mechanical Engineering (AREA)
- Geochemistry & Mineralogy (AREA)
- Earth Drilling (AREA)
- Steroid Compounds (AREA)
- Pistons, Piston Rings, And Cylinders (AREA)
- Fluid-Damping Devices (AREA)
- Mutual Connection Of Rods And Tubes (AREA)
- Dowels (AREA)
Abstract
A threaded coupling for a high frequency percussion drill assembly comprises a rod and a sleeve having external and internal threads, respectively. The threads are of the asymmetrical type and make contact along opposing shoulder portions disposed on only one side of each crown portion. The threads have a maximum diameter from 30 to 40 mm, a pitch of 7 to 11 mm, and a height from 1.2 to 1.6 mm. The parts of the root and crown portions located immediate adjacent the contacting shoulder portions have radii from 3 to 5 mm.
Description
The present invention relates to a threaded coupling having a diameter in the interval of 30 to 40 mm adapted for percussion drill rods and comprising an external thread on the rod and an internal thread in the sleeve, the threads both of the rod and the sleeve having continuously curved tops and bottoms in the longitudinal section of said threads.
In drill steel couplings a type of rope thread called the R16-profile has been used for a long time. In equipment for drifter drilling it is totally dominating.
The R16-profile has a good fatigue resistance in combination with a satisfying wearability thanks to the rounded shape of tops and bottoms of the thread.
It has however turned out that the R16-profile does not function in a satisfying way together with the high frequency percussive drilling machines that have been developed during recent years.
The problem is that the thread coupling due to the high percussion frequency does not stay sufficiently tightened during work. This means that the degree of efficiency for the energy of the shock wave decreases and so-called pittings develop on the contact surfaces of the thread. These pittings do eventually lead to a fatigue fracture.
The aim of the invention is thus to prevent a thread coupling that remains sufficiently tightened during work without deteriorating the good characteristics in fatigue resistance and wearability.
Below, an embodiment of the invention will be described with reference to the accompanying drawings where FIGS. 1a and 1b disclose certain geometric parameters in connection with threads; FIG. 2 discloses schematically the geometry of a so-called rope thread; FIGS. 3a and 3b disclose a diagram of how the tightening capacity varies with the pitch and the shoulder angle.
When designing the concept to be valid for a thread coupling according to the present invention the following has been taken into consideration.
The tightening capacity of a thread can be defined as the ratio between the uncoupling torque, MU, and the tightening torque, MT.
For an arbitrary thread the following is valid: ##EQU1##
The geometric quantities of the formula (1) are disclosed in FIGS. 1a and 1b. A characterizing feature for rope threads is that they have a constant radius of curvature both at the thread top and its bottom. In FIG. 2 these constant radii of curvature are designated by R1 and R2, respectively.
From FIG. 2 the following formula can be learnt:
(H--R.sub.1 --R.sub.2) sin (β/2)-S/2 cos (β/2)+R.sub.1 +R.sub.2 =0 (2)
where
H=the thread height
S=the pitch
β/2=the shoulder angle
By combining the formulas (1) and (2) it is possible to optimize the tightening capacity ##EQU2## for a rope thread. For a known rope thread having so-called R16-profile and a diameter of 38 mm a value for ##EQU3## =0.66 is achieved if the formulas (1) and (2) are combined and μ is given the value of 0.2 that empirically has been found to be a normal value for threaded drill steel couplings.
The primary aim of the present invention is thus to increase the tightening capacity of a thread coupling, i.e. ##EQU4## shall relatively seen have as high a value as possible. However, in order not to affect, to a too great extent, the characteristics concerning fatigue resistance and wearability in a negative way, one must also consider the relative magnitude of the height and radius of curvature of the thread.
The embodiment according to FIGS. 3a and 3b refers to a so-called asymmetrical thread, the thread coupling having a maximum diameter DyM of 38 mm.
Although the above disclosed formula (2) refers to rope threads the ideas of the present invention also are applicable in an asymmetrical thread coupling according to FIGS. 3a and 3b. The reason for that is that contact only is present along one 16R, 16S of the thread shoulders 16R, 16S, 17R, 17S that are located on both sides of each top or bottom of each thread, respectively. In the disclosed embodiment contact will be present only along the shoulder that is most leveled, i.e. has the smallest inclination, said shoulder and the adjacent portion of the adherent top and bottom up to its highest and lowest point, resp., constitute "half" a rope thread. Since a decreased pitch generally seen leads to a higher value of the tightening property ##EQU5## the shoulder that has no contacting function in the thread coupling is made as short as possible. Compared to a conventional rope thread the asymmetrical thread according to FIGS. 3a and 3b has the advantage of a relatively seen smaller pitch S that leads to a better tightening property than a conventional rope thread having the same parameters for the working thread shoulder, i.e. where contact is present.
For the embodiment according to FIGS. 3a and 3b the external thread on the rod 10R according to FIG. 3a has a height H1 equal to 1.50 mm, the pitch S is equal to 9.28 mm, the radius of curvature R1 for the top or crown 12R of the thread is 3.5 mm, and the radius of curvature R2 for the bottom or root 14R of the thread is 4.0 mm.
The internal thread of the sleeve 10S according to FIG. 3b has a height H2 of 1.435 mm, a pitch S of 9.28 mm, a radius of curvature R3 for the top 12S of thread of 5.0 mm, and a radius of curvature R4 for the bottom 14S of the thread of 3.5 mm.
The diagram of FIG. 4 discloses how the tightening capacity ##EQU6## varies with the parameters for pitch S and shoulder angle, said angle in itself including the parameters of radius of curvature and height.
In FIG. 4 the tightening capacity ##EQU7## has been calculated for different values of pitch and shoulder angle; each curve (continuous or dotted) refers to constant radii of curvature that coincide with the radii of curvature both for the known thread so-called R16-profile as well as for the new threads according to FIGS. 3a and 3b in the present application. In this connection it has been assumed that μ=0.2.
The points inserted in FIG. 4 correspond to the values of pitch and shoulder angle that the R16-profile and the threads according to FIGS. 3a and 3b have been given. It should be noticed that the intention is to be located in the area of the curve where the tightening capacity ##EQU8## is as high as possible.
Claims (5)
1. A threaded coupling for a high-frequency percussion drill assembly comprising a rod and a sleeve,
said rod comprising an external thread having continuously curved crown and root portions interconnected by shoulder portions,
said sleeve comprising an internal thread having continuously curved crown and root portions interconnected by shoulder portions arranged to oppose respective ones of said shoulder portions of said external thread,
said internal and external threads each being of asymmetrical configuration so as to make contact along opposing shoulder portions disposed on only one side of each crown portion,
said external thread having a maximum diameter in the range of 30 to 40 mm, a pitch in the range of 7 to 11 mm, and a height in the range of 1.2 to 1.6 mm, the parts of said root and crown portions located immediately adjacent the contacting shoulder portions having radii in the range of 3 to 5 mm, said internal thread having a maximum diameter in the range of 30 to 40 mm, a pitch in the range of 7 to 11 mm, and a height in the range of 1.2 to 1.6 mm, and the parts of said root and crown portions located immediately adjacent the contacting shoulder portions having radii in the range of 3 to 5 mm.
2. A threaded coupling according to claim 1, wherein said pitch of said internal and external threads is in the range of 8 to 10 mm.
3. A threaded coupling according to claim 1, wherein said height of said internal and external threads is in the range of 1.3 to 1.5 mm.
4. A threaded coupling according to claim 1, wherein said internal and external threads have a pitch in the range of 9.2 to 9.3 mm, and a height in the range of 1.4 to 1.5 mm, and a radius of curvature of said parts of said root and crown portions being in the range of 3.5 to 5 mm.
5. A threaded coupling according to claim 4, wherein said maximum diameter of said internal and external threads is 38 mm.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
SE8603118A SE460550B (en) | 1986-07-15 | 1986-07-15 | THREADED CONNECTOR FOR BEAM SHUTTER |
SE8603118 | 1986-07-15 |
Publications (1)
Publication Number | Publication Date |
---|---|
US4861209A true US4861209A (en) | 1989-08-29 |
Family
ID=20365113
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US07/073,801 Expired - Fee Related US4861209A (en) | 1986-07-15 | 1987-07-14 | Threaded coupling |
Country Status (10)
Country | Link |
---|---|
US (1) | US4861209A (en) |
EP (1) | EP0253789B1 (en) |
JP (1) | JPS6367418A (en) |
AT (1) | ATE82615T1 (en) |
CA (1) | CA1291880C (en) |
DE (1) | DE3782688T2 (en) |
FI (1) | FI86664C (en) |
IE (1) | IE60576B1 (en) |
SE (1) | SE460550B (en) |
ZA (1) | ZA874990B (en) |
Cited By (13)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5060740A (en) * | 1990-05-29 | 1991-10-29 | Sandvik Rock Tools, Inc. | Screw thread coupling |
US5163513A (en) * | 1991-06-28 | 1992-11-17 | Bowen Tools, Inc. | Circle threadform for marine riser top joint |
AU753562B2 (en) * | 1998-09-28 | 2002-10-24 | Epiroc Drilling Tools Aktiebolag | Thread coupling for a drill string for percussive rock drilling |
US20050161259A1 (en) * | 2004-01-26 | 2005-07-28 | Anmol Kaul | Unsymmetrical profile threads for use in a positive displacement motor housing |
US7575024B2 (en) | 2005-11-05 | 2009-08-18 | Snap-Tite Technologies, Inc. | Threaded coupling with flow shutoff |
US7762279B2 (en) | 2005-11-05 | 2010-07-27 | Snap-Tite Technologies, Inc. | Threaded coupling with flow shutoff |
US20110084482A1 (en) * | 2008-04-02 | 2011-04-14 | Bronswerk Radiax Technology B.V. | Conical Screw Coupling |
US20180023611A1 (en) * | 2015-02-27 | 2018-01-25 | Dreco Energy Services Ulc | Thread profiles for rotary shouldered connections |
EP3536893A1 (en) | 2018-03-09 | 2019-09-11 | Sandvik Mining and Construction Tools AB | Connection for percussion drilling |
EP3663506A1 (en) | 2018-12-03 | 2020-06-10 | Sandvik Mining and Construction G.m.b.H. | A drilling string, threaded coupling, and rod adaptor for rotary drilling |
WO2020161542A1 (en) | 2019-02-06 | 2020-08-13 | James Jing Yao | Threaded coupling for percussion drill bit |
WO2020247923A1 (en) * | 2019-06-06 | 2020-12-10 | Fermata Technologies, Llc | Arcuate thread form fit |
US11598159B2 (en) * | 2018-03-09 | 2023-03-07 | Sandvik Mining And Construction Tools Ab | Coupling for connecting downhole tubulars |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JP2024507382A (en) * | 2021-02-26 | 2024-02-19 | サンドヴィック マイニング アンド コンストラクション ツールズ アクティエボラーグ | Connector for connecting downhole pipes with reduced stress |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1953095A (en) * | 1931-07-18 | 1934-04-03 | Timken Roller Bearing Co | Detachable bit |
GB629837A (en) * | 1947-11-08 | 1949-09-29 | Hall & Pickles Ltd | Improvements in percussive drilling tools |
US3586353A (en) * | 1969-01-13 | 1971-06-22 | Howard I Lorenz | Thread arrangement for earth boring members |
US3645570A (en) * | 1970-05-04 | 1972-02-29 | Sandvikens Jernverks Ab | Coupling thread for percussion drill rods |
US4295751A (en) * | 1978-09-21 | 1981-10-20 | Boart International Limited | Thread structure for percussion drill elements |
Family Cites Families (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US27284A (en) * | 1860-02-28 | Office | ||
US3966341A (en) * | 1974-12-16 | 1976-06-29 | Joy Manufacturing Company | Drill steel |
-
1986
- 1986-07-15 SE SE8603118A patent/SE460550B/en not_active IP Right Cessation
-
1987
- 1987-07-07 EP EP87850221A patent/EP0253789B1/en not_active Expired - Lifetime
- 1987-07-07 DE DE8787850221T patent/DE3782688T2/en not_active Expired - Fee Related
- 1987-07-07 AT AT87850221T patent/ATE82615T1/en not_active IP Right Cessation
- 1987-07-08 ZA ZA874990A patent/ZA874990B/en unknown
- 1987-07-13 FI FI873102A patent/FI86664C/en not_active IP Right Cessation
- 1987-07-14 US US07/073,801 patent/US4861209A/en not_active Expired - Fee Related
- 1987-07-14 JP JP62174020A patent/JPS6367418A/en active Pending
- 1987-07-14 IE IE189487A patent/IE60576B1/en not_active IP Right Cessation
- 1987-07-14 CA CA000541944A patent/CA1291880C/en not_active Expired - Lifetime
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US1953095A (en) * | 1931-07-18 | 1934-04-03 | Timken Roller Bearing Co | Detachable bit |
GB629837A (en) * | 1947-11-08 | 1949-09-29 | Hall & Pickles Ltd | Improvements in percussive drilling tools |
US3586353A (en) * | 1969-01-13 | 1971-06-22 | Howard I Lorenz | Thread arrangement for earth boring members |
US3645570A (en) * | 1970-05-04 | 1972-02-29 | Sandvikens Jernverks Ab | Coupling thread for percussion drill rods |
US4295751A (en) * | 1978-09-21 | 1981-10-20 | Boart International Limited | Thread structure for percussion drill elements |
Cited By (20)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5060740A (en) * | 1990-05-29 | 1991-10-29 | Sandvik Rock Tools, Inc. | Screw thread coupling |
US5163513A (en) * | 1991-06-28 | 1992-11-17 | Bowen Tools, Inc. | Circle threadform for marine riser top joint |
AU753562B2 (en) * | 1998-09-28 | 2002-10-24 | Epiroc Drilling Tools Aktiebolag | Thread coupling for a drill string for percussive rock drilling |
US6810956B1 (en) | 1998-09-28 | 2004-11-02 | Uniroc Ab | Thread coupling for a drill string for percussive rock drilling |
US20050161259A1 (en) * | 2004-01-26 | 2005-07-28 | Anmol Kaul | Unsymmetrical profile threads for use in a positive displacement motor housing |
US7575024B2 (en) | 2005-11-05 | 2009-08-18 | Snap-Tite Technologies, Inc. | Threaded coupling with flow shutoff |
US7762279B2 (en) | 2005-11-05 | 2010-07-27 | Snap-Tite Technologies, Inc. | Threaded coupling with flow shutoff |
US20110084482A1 (en) * | 2008-04-02 | 2011-04-14 | Bronswerk Radiax Technology B.V. | Conical Screw Coupling |
US8696285B2 (en) * | 2008-04-02 | 2014-04-15 | Bronswerk Radiax Technology B.V. | Conical screw coupling |
US10767683B2 (en) * | 2015-02-27 | 2020-09-08 | Dreco Energy Services Ulc | Thread profiles for rotary shouldered connections |
US20180023611A1 (en) * | 2015-02-27 | 2018-01-25 | Dreco Energy Services Ulc | Thread profiles for rotary shouldered connections |
EP3536893A1 (en) | 2018-03-09 | 2019-09-11 | Sandvik Mining and Construction Tools AB | Connection for percussion drilling |
WO2019170437A1 (en) | 2018-03-09 | 2019-09-12 | Sandvik Mining And Construction Tools Ab | Connection for percussion drilling |
US11598159B2 (en) * | 2018-03-09 | 2023-03-07 | Sandvik Mining And Construction Tools Ab | Coupling for connecting downhole tubulars |
EP3663506A1 (en) | 2018-12-03 | 2020-06-10 | Sandvik Mining and Construction G.m.b.H. | A drilling string, threaded coupling, and rod adaptor for rotary drilling |
WO2020114699A1 (en) | 2018-12-03 | 2020-06-11 | Sandvik Mining And Construction G.M.B.H. | A drilling string, threaded coupling, and rod adaptor for rotary drilling |
US12000215B2 (en) | 2018-12-03 | 2024-06-04 | Sandvik Mining And Construction G.M.B.H. | Drilling string, threaded coupling, and rod adaptor for rotary drilling |
WO2020161542A1 (en) | 2019-02-06 | 2020-08-13 | James Jing Yao | Threaded coupling for percussion drill bit |
WO2020247923A1 (en) * | 2019-06-06 | 2020-12-10 | Fermata Technologies, Llc | Arcuate thread form fit |
US11396962B2 (en) | 2019-06-06 | 2022-07-26 | Fermata Technologies, Llc | Arcuate thread form fit |
Also Published As
Publication number | Publication date |
---|---|
SE8603118D0 (en) | 1986-07-15 |
FI86664B (en) | 1992-06-15 |
IE60576B1 (en) | 1994-07-27 |
CA1291880C (en) | 1991-11-12 |
DE3782688D1 (en) | 1992-12-24 |
EP0253789A2 (en) | 1988-01-20 |
FI873102A (en) | 1988-01-16 |
IE871894L (en) | 1988-01-15 |
SE8603118L (en) | 1988-01-16 |
EP0253789A3 (en) | 1989-03-22 |
FI86664C (en) | 1992-09-25 |
FI873102A0 (en) | 1987-07-13 |
ATE82615T1 (en) | 1992-12-15 |
EP0253789B1 (en) | 1992-11-19 |
JPS6367418A (en) | 1988-03-26 |
ZA874990B (en) | 1988-01-14 |
DE3782688T2 (en) | 1993-04-01 |
SE460550B (en) | 1989-10-23 |
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Legal Events
Date | Code | Title | Description |
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AS | Assignment |
Owner name: SANDVIK AB, S-811 81 SANDVIKEN, SWEDEN, A CORP. OF Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:LARSSON, KENNETH L.;REEL/FRAME:004784/0893 Effective date: 19870814 |
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Free format text: PAYOR NUMBER ASSIGNED (ORIGINAL EVENT CODE: ASPN); ENTITY STATUS OF PATENT OWNER: LARGE ENTITY |
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Effective date: 19970903 |
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STCH | Information on status: patent discontinuation |
Free format text: PATENT EXPIRED DUE TO NONPAYMENT OF MAINTENANCE FEES UNDER 37 CFR 1.362 |